Ordered mesoporous silica can be synthesized in a variety of pore sizes, pore shapes and morphologies. Due to its potential applications in e.g. separation, catalysis, adsorption and as a template, this group of materials has received much interest the last decades. Depending on the application various morphologies, pore sizes and pore shapes are preferred.
One example of mesoporous silica is SBA-15. SBA-15 with its hexagonally ordered cylindrical pores can be synthesized in a variety of morphologies e.g. fibers, spheres, platelets or monodispersed rods. Wang et al in Mater. Chem. Phys, 115(2009) 649-655 discloses SBA-15 rods with different lengths. Si-compounds are polymerized to larger structures. HCl concentrations of 2.5, 2.0, 1.0, and 0.5 M were tested and no big differences were found. In FIG. 6 of Wang et al it can be seen that a high acidity leads to shorter structures. Glycerol is stated to play an important role for the controlled formation of rods according to the teachings for instance at the end of section 3.2.
The pore size of SBA-15 is normally 6-9 nm but it can be increased by e.g. adding swelling agents such as 1,3,5-trimethylbenzene (TMB) or by varying the hydrothermal treatment time and temperature. Increasing the pore size using swelling agent is possible up to a certain limit, but due to a phase transition from ordered hexagonal pores to disordered mesocellular foams this is the maximum pore size obtained. Low temperature syntheses with alkanes and NH4F can increase the pore size where the morphology can be varied by varying synthesis parameters.
E. Johansson et al in Microporous and Mesoporous Materials, volume 133, issue 1-3, pages 66-74, September 2010 discloses manufacture of mesoporous silica in the form of crystallites with hexagonally arranged pores running through the crystallites. The crystallites are always attached to each other. The crystallites can be attached end-to-end to form fibers, or the crystallites can be attached side-by-side to form sheets. It is disclosed that heptane in the presence of NH4F works as a pore swelling agent. The HCl concentration was varied between 1.37-1.98 M.
E. Johansson et al in Materials Letters, volume 63, Issue 24, pages 2129-2131, October 2009 discloses mesoporous silica in the form of crystallites attached side-by-side to sheets, where the pores are parallel to the sheet normal.
A problem in the state of art is how to separate the crystallites so that they are suitable for further use. It is also a problem in the prior art that the time for the synthesis is rather long.